How to make table with different columns per row?
Try this:
\documentclass{article}
\usepackage{sans}
\renewcommand{\arraystretch}{1.3}
\begin{document}
\begin{table}
\begin{tabular}{|c|c|c|c|c|c|}
\hline
& \multicolumn{4}{|c|}{Display Format}& \\ \cline{2-5}
&\multicolumn{2}{|c|}{High information density}& \multicolumn{2}{|c|}{Low information density} &\\ \hline
Cookie type & Noticeable& Non-noticeable& Noticeable& Non-noticeable& Total \\ \hline
1\textsuperscript{st} - party cookies&29&17&27&20&93\\ \hline
1\textsuperscript{st}/3\textsuperscript{rd} party cookies&19&22&23&20&84\\ \hline
Total& 48&39&50&40&177\\ \hline
\end{tabular}
\caption{Number of respondants for treatment}
\end{table}
\end{document}
and image of table obtained by above code:
Your table is going to be very huge ... 24 cm wide :)- See if the following is what you looking for:
\documentclass{article}
\usepackage{array}
\begin{document}
\begin{table}[h]
\renewcommand\arraystretch{1.3}
\begin{tabular}{|l | *{4}{>{\centering}p{2cm}|}c|}
%{|m{4cm}|m{4cm}|m{4cm}|m{4cm}|m{4cm}|m{4cm}}
\hline
& \multicolumn{4}{c|}{Display Format}
& \\
\hline
Cookie type
& \multicolumn{2}{c|}{High information-density}
& \multicolumn{2}{c|}{Low information-density}
& Total \\
\hline
1\textsuperscript{st} party cookies
& 29 & 17 & 27 & 20 & 93 \\
\hline
\end{tabular}
\caption{Number of respondents per treatment}
\label{table:3}
\end{table}
\end{document}